1. Field of the Invention
The present invention relates generally to cellular telecommunications systems and methods, and specifically to home location registers within cellular telecommunications systems.
2. Description of Related Art
A conventional cellular network is made up of a plurality of areas, each with a Mobile Switching Center (MSC) and Visitor Location Register (VLR) therein. The VLR is a database maintaining information about each of the mobile subscribers currently located within the MSC/VLR area. The MSC provides a circuit switched connection of speech and signaling information between a Mobile Station (MS) and the network. It should be understood that, as termed herein, the MS is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network, each other, and users outside the subscribed network, both wireline and wireless.
The MSC/VLR areas, in turn, include a plurality of Location Areas (LA), which are defined as that part of an MSC/VLR area in which the MS may move freely without having to send update location information to the MSC that controls the LA. Each LA is further divided into a number of cells. Each cell includes a base station, which is responsible for providing radio coverage to the cell. Signaling information and voice or data is transmitted between the base station and the MS over the air interface.
The cellular network also includes a Home Location Register (HLR), which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information, for subscribers registered within that network. The HLR may be standalone or co-located with a given MSC, integrated with the MSC, or alternatively can service multiple MSC""s.
Each base station broadcasts the LA associated with the cell that the base station is located in. Each MS stores the current LA therein. When the MS determines that the LA has changed from the stored LA, the MS performs a location registration.
With reference now to FIG. 1 of the drawings, which will be described in connection with FIG. 2 of the drawings, the signaling involved in a typical location registration process is illustrated. Upon receiving a location registration request from an MS 10 (step 200), the MSC 20b requests subscriber data associated with that MS 10 from the HLR 30 (step 210). In response, the HLR 30 transmits the requested subscriber data back to the MSC 20b (step 220), which uses the subscriber data to authenticate the MS 10 (steps 230 and 240). Thereafter, the MSC 20b updates the HLR 30 with the new MSC 20b identity information (step 250), which is used by the HLR 30 to route incoming calls to the MS 10. The HLR 30 acknowledges the receipt of the new MSC 20b identity to the MSC 20b (step 260), which in turn, acknowledges the registration request to the MS 10 (step 270). Finally, the HLR 30 informs the old MSC 20a that the MS 10 was previously registered with that the MS 10 has left the old MSC 20a, and instructs the old MSC 20a to erase the MS 10 subscriber data from it""s VLR (steps 280 and 290).
After a system restart in an MSC or upon first initialization of the MSC, the MSC is typically accessed by a large number of MS""s requesting location registration, since the broadcasted LA information that the MS receives has changed (due to e.g. the MS moving to a new LA or reorganization of the LA""s) to the new LA""s that the MSC serves. For PDC systems, at restart, the MS""s at the MSC service border roam to the neighboring MSC while the serving MSC is down and roam back when service is available again. This means that a large number of subscriber data requests and MSC identity signals may be sent from the MSC to the HLR, which may overload the central processor (CP) in the HLR.
The signaling between the MSC and the HLR is implemented on the Mobile Application Protocol (MAP) MAP uses the Mobile Transport Protocol (MTP) as the transport mechanism. MTP includes, as by defined by CCITT7 for Signaling System No. 7, a Link Status Signaling Message Unit (LSSU) with a Status Indication (SI) field, which is used for a Status Indication Busy (SIB) code, that can be sent from the HLR to the MSC if signaling at the HLR receiving end is congested due to, for example, HLR CP overload. The SIB signal stops all signaling towards the HLR, and is sent in short intervals ( less than 1 second) as long as the HLR is congested. When the HLR overload condition ceases, the HLR discontinues the sending of the SIB signal.
However, even though the SIB signal forces a complete stoppage of the signaling between the MSC and the HLR, the MSC will still receive a large number of location registration requests. Therefore, when the SIB signal ceases, the signaling will be as intensive as before the stoppage. This will lead to additional stoppages, resulting in a toggling effect. This regulation method is not efficient for traffic handling, nor is it an efficient usage of the MSC and HLR CP capacity.
A registration can be interrupted and rejected due to HLR congestion at two occasions. The first occasion is when the MAP signal xe2x80x9cSubscriber Data Requestxe2x80x9d is sent from the MSC to the HLR. The second time is when the MAP signal xe2x80x9cLocation Registrationxe2x80x9d is sent from the MSC to the HLR. In both of these cases, the MAP send buffer may be congested and the signaling request rejected.
The registration process in the new MSC 20b as presented in FIG. 1 typically uses 5% of the CP capacity during normal busy hour conditions. In certain circumstances, such as system restart, the load in the MSC may increase up to and over the loadability limit (around 95% of the CP capacity) of the MSC. Around 70% of this load may occur due to registration processing as specified in FIG. 1. The registration load is high in the surrounding MSC""s as well, due to the roaming between MSC""s, as described previously.
The registration process uses up to 70% of the CP capacity typically used by a successful registration towards the HLR in the MSC when the registration process is interrupted and a registration reject signal is replied to the mobile due to HLR congestion. This percentage of CP capacity is ultimately wasted. For example, if the first signaling attempt is rejected due to HLR congestion, 25% of the CP capacity needed in the MSC for a complete registration may have already been used. If the second signaling attempt is rejected due to HLR congestion, up to 82% of the CP capacity needed in the MSC for a complete registration may have been used.
Likewise, in the HLR, approximately 50% of the CP capacity for a complete registration may already have been used for a registration that is later rejected due to congestion. For example, if the second MAP signal is rejected, that registration attempt has typically already used 43% of the CP capacity needed for a complete registration in the HLR, by processing the first MAP message. As such, that CP capacity already used in the HLR, has been wasted. As a whole, if 50% of the MAP signals congested by the HLR are first MAP messages and 50% are second MAP messages, then 22% of the CP capacity needed for a complete registration in the HLR has been wasted on average.
It is, therefore, an object of the present invention to efficiently regulate the traffic conditions in the MSC and HLR to prevent an HLR overload condition.
It is a further object of the present invention to reduce, but not eliminate, the number of registration requests sent by the MSC to the HLR based on the current load in the HLR to protect against an HLR overload condition.
The present invention is directed to telecommunications systems and methods for managing congestion in the HLR. At regular intervals or in response to receiving a registration message, the HLR can transmit the current load conditions in the HLR to one or more MSC""s within the area served by the HLR. In response, the MSC""s can use this load information to reduce the registration intensity in order to protect the HLR from congestion. Each MSC can include one or more HLR load thresholds, and if the current load level in the HLR is above one of these thresholds, the MSC can reduce the number of registration messages sent to the HLR by a certain amount. This can be accomplished by the MSC intelligently discarding or restricting new registration requests originating from the MS""s served by the MSC. Alternatively, the HLR can store the threshold information for each MSC within the area served by the HLR, and transmit an access rate (reduction amount of registration requests) to each MSC, which can use this information to discard or restrict new registration requests.